The present invention relates to a fluid supply system and, more particularly, to a system for filtering fluid to an ink jet print head at a substantially constant flow rate.
Typically, an ink jet printer, such as of the type shown in U.S. Pat. No. 3,701,998, issued Oct. 31, 1972, to Mathis, produces a plurality of jet drop streams which are directed at a print receiving medium for depositing drops on the medium in a predetermined pattern, thus producing collectively a print image on the print medium. A print head, defining a fluid receiving reservoir, receives ink under pressure such that the ink flows through a plurality of orifices defined by an orifice plate communicating with the reservoir, thereby producing the jet drop streams. The drops in these jet drop streams may be selectively charged, with charged drops being deflected by an electrostatic field to one or more catchers. Uncharged drops are not deflected and, therefore, strike the print receiving medium. By appropriate selective charging of the drops, the desired image may be formed on the medium.
Most ink jet printers include an ink supply system having an arrangement for reusing ink which is caught by the printer catchers. Since the environment in which an ink jet printer operates typically includes substantial amounts of dust and other particles, it will be appreciated that such particles may contaminate the ink returned from the catchers to the ink supply system. It is necessary, therefore, to provide for filtering the ink prior to supplying it to the print head.
Additionally, it is important that the ink be supplied to the print head under a substantially constant pressure. Prior art printers, such as that shown in Mathis, have typically included a pressure gauge or other pressure measuring means communicating directly with the print head reservoir. This may be somewhat disadvantageous in that ink particles and contaminate particles may tend to accumulate around the pessure gauge and thereafter be dislodged into the ink as larger particles may cause clogging of the orifices. While this problem may be eliminated by measuring the pressure of the ink further upstream in the ink supply system, if filters between the print head reservoir and the point at which the pressure measurement is made become partially blocked, the pessure measurement will not provide an accurate indication of the actual ink pressure in the print head.
A number of ink supply systems have been developed in the past for use with ink jet printers. One such system, disclosed in U.S. Pat. No. 3,761,953, issued Sept. 25, 1973, to Helgeson, provides for continuous ink recirculation through the supply system. Ink is supplied to the jet printer from a pressure reservoir which, in turn, is supplied from a fluid pump. Overflow from the pressure reservoir is continuously returned to the pump. Additionally, a filter is provided in the recirculating ink path from the pump to the pressure vessel to filter particles from the ink.
U.S. Pat. No. 4,011,157, issued Mar. 8, 1977, to Pennebaker et al., discloses an ink jet supply system including an arrangement by which impurities contaminating recirculating ink are removed by subjecting the contaminated ink to ultrasonic energy to form an ink aerosol. The aerosol is entrained in an air stream and carried to an impactor where it is caused to return to a liquid state. Ink is then supplied from the impactor to the printer. The aerosol which is produced is said to be substantially free of impurities greater than 1 micron in size.
U.S. Pat. No. 4,079,384, issued Mar. 14, 1978, to Takano et al., discloses an ink supply system for an ink jet printer having a recirculating ink path incorporating a pump, a main filter, and an ink reservoir. Ink is diverted from this recirculating path to the ink jet printer by means of an electromagnetic cross valve. None of the above noted ink supply systems incorporates an arrangement by which the ink flow to the print head from the recirculating ink path may be regulated. Additionally, these references do not suggest monitoring print head fluid pressure other than by measuring pressure directly in the print head or in the print head supply line.
Other ink jet supply systems incorporate nonrecirculating pump and filter devices which supply the print head. Such an arrangement is disclosed in U.S. Pat. No. 3,929,071, issued Dec. 30, 1975, to Cialone et al. Ink, which is collected in a gutter associated with the ink jet nozzle, is returned to an ink supply bottle for reapplication to the nozzle. The ink is therefore filtered only once during each passage through the system and the ink in the supply system is not moving when the printer is not in operation. This may create undesired deposit of particle contaminants at various points in the system.
Other fluid supply systems, not specifically designed for use with an ink jet printer, have included a recirculating fluid loop between a pump, filter, and fluid reservoir for continuously circulating fluid through the filter. Fluid is removed from this loop as required. As shown in U.S. Pat. No. 3,389,797, issued June 25, 1968, to Giardini, and U.S. Pat. No. 3,502,213, issued Mar. 24, 1970, to Kuribayashi, such systems have included a centrifugal filter in which a mainstream fluid path is provided through the filter along the surface of a filter element. Filtrate passes through the filter element and is thereafter removed from the supply loop while the mainstream effluent washes the surface of the filter element. Additionally, any particles carried by the unfiltered fluid generally have sufficient inertia such that they are not drawn through the filter element. The Giardini and Kuribayshi systems, however, do not provide for control of the filtered fluid output of the system.
Accordingly, it is seen that there is a need for a fluid supply system for an ink jet printer in which fluid is continuously recirculated through a supply loop including a filter, and in which the fluid is controllably removed from the supply loop and applied to the print head of the printer.